The present invention relates to an electronic control device.
For example, as disclosed in Japanese Laid-Open Patent Publication No. 2005-150633, an electronic control device for a vehicle is provided with a box-shaped casing, and an electronic circuit substrate on which electronic components are mounted is accommodated within the casing. Further, in most cases, an upper portion of the casing is provided with a heat sink for radiating heat generated from the electronic components to an external portion.
Normally, the heat sink is formed by a metal having a high heat radiation performance (high heat conductivity). As shown in FIG. 8, a plurality of heat radiation fins 41 are provided on an upper surface 40a of a heat sink 40 in order to increase a surface area. Accordingly, the heat radiation performance of the heat sink 40 is improved.
Conventionally, there has been required to effectively utilize a restricted space in a vehicle. Further, electronic control devices are required to add to flexibility in the arrangement. In other words, there are cases in which an electronic control device is covered with salt water or muddy water at a time of traveling, or the casing is mounted at a position which is completely submerged in water. Accordingly, various types of waterproofing are applied to the casing of electronic control devices.
However, since the heat sink is not used in a place which tends to get wet with water, no special waterproofing has been applied to heat sinks. Accordingly, in the case that a heat sink gets wet with muddy water or salt water, the heat radiation performance of the heat sink is lowered by corrosion or foreign material such as mud or the like.